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DERIVATIVES AND HEDGING ACTIVITIES - Credit Risk Related Contingent Features (Details) - USD ($) | 3 Months Ended
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Mar. 31, 2022 | Mar. 31, 2021
Credit Risk Related Contingent Features [Abstract] |  |
Derivatives in a net liability position | $ 0 |
Termination value of derivatives | $ 0 | $ 785,000,000.0
Number of provisions breached | 0 |

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- References No definition available. + Details
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- Definition Refers to the number of provisions of a derivative obligation agreement between the entity and a counterparty breached by the entity. + References No definition available. + Details
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Namespace Prefix: | dcom_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Definition The value of a terminated derivative instruments. + References No definition available. + Details
Name: | dcom_DerivativeTerminationValue
Namespace Prefix: | dcom_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4H -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5624258-113959 + Details
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Balance Type: | credit
Period Type: | instant